[[File:Pneumonia.jpg|thumb|350px|left|Pneumonia]]Pneumonia is an infection that inflames the air sacs in one or both lungs. The air sacs may fill with fluid or pus, causing cough with phlegm or pus, fever, chills and difficulty breathing. A variety of organisms, including bacteria, viruses and fungi, can cause pneumonia. Pneumonia can range in seriousness from mild to life-threatening. It is most serious for infants and young children, people older than age 65, and people with underlying health problems or weakened immune systems.
== Symptoms ==
Pneumonia is an inflammation of the lung parenchyma commonly caused by microbial agents (Johnson, MS 11th Ed.). The inflammatory reactions may occur in the alveoli, giving rise to exudates that partly blocks the alveoli or bronchi. Thus, bronchospasm may occur when the patient has a reactive airway illness that may hinder the gas exchange.
Symptoms of pneumonia include sudden chills, increasing fever (38.5 to 40.5 degree Celsius) and profuse sweating. Occurrence of chest pain may be noted and is aggravated by breathing and coughing and in severe cases tachypnea (rapid breathing) is noticeable, ranging from 25 to 45 breaths per minute coupled with a difficulty of breathing. Headache, myalgia (muscle pains), and upper respiratory tract symptoms such as nasal congestion and sore throat may be initialized too.